CORC^® wires containing integrated optical fibers for temperature and strain monitoring and voltage wires for reliable quench detection

Abstract

Safe operation of large superconducting magnets wound from high-temperature superconductors (HTS) requires reliable detection of the onset of a quench. A novel method to integrate optical fibers and voltage wires within the core of multi-tape HTS CORC ® wires has been developed that allows real time monitoring of local changes in strain, temperature and of the superconducting state of the magnet windings. The ability to detect highly localized changes in temperature with Rayleigh scattering in the embedded optical fibers provides invaluable information about local heating at hot spots from which a quench may originate. Integrated voltage contacts allow accurate voltage measurements in long CORC ® wires without being affected by high current ramp rates or electromagnetic interference. They also allow detection of inductively driven redistribution of current between tapes in CORC ® wires that may occur at high current ramp rates. Continuous monitoring of temperature and voltage was used to detect the formation of local hot spots induced by a heater or by operating the CORC ® wire above its critical current. The results show that, within the boundary conditions of the experiment and the method by which the optical fibers were integrated into the CORC ® wire in this study, the speed and resolution with which hot spots can be detected with optical fibers lagged that of the integrated voltage wires. This study also shows that integrated voltage wires reliably detected the formation of a local hot spot in a 5.1 meter long coiled CORC ® wire, down to a hot spot size covering 0.1% of the conductor length and at current ramp rates as high as 2000 A s −1 . Voltage measurements thus remain an effective option for quench detection in magnets wound with HTS conductors for which current sharing between tapes allows for operation within the flux flow regime.

Advancing Superconducting Magnet Diagnostics for Future Colliders

“…Indeed, Rayleigh-scattering based fibers were used to detect the temperature change with a high spatial resolution in the millimeter range [46]. Fibers have been also integrated into a REBCO conductor architecture and demonstrated strain sensing capabilities as well as thermal perturbation detection and localization with higher spatial resolution than voltage taps [15,50,51]. More R&D development will be necessary for employment of Rayleigh distributed sensors in superconducting magnets.…”

Distributed Fiber Optic Sensing to Identify Locations of Resistive Transitions in REBCO Conductors and Magnets

“…The same technology was demonstrated to have a similar sensitivity at 77 K and room temperature in a subsequent study [14]. More recently, the OFDR technology was tested with an optical fiber embedded inside a REBCO CORC ® cable for quench detection [15] [16].…”

“…Although the fiber optic sensing shows a mixed performance for quench detection due to a stringent temporal resolution and high sensitivity to local heating [15][16][17], the distributed sensing capability of fiber optic remains attractive to address our need to identify the locations of initial flux-flow voltages in multi-tape REBCO cables and magnets.…”

Strain Transfer Function of Distributed Optical Fiber Sensors and Back-Calculation of the Base Strain Field

“…They show high potential not only for structural health monitoring, but also for sensing temperature, acoustic waves, electric and magnetic fields, or chemicals, amongst other applications, owing to attractive features such as lightweight, small size, immunity to electromagnetic interference, and non-corrosive features [ 2 , 6 ]. Recently, optical fiber sensors attract great attention in measuring strain and temperature changes in cryogenic environments [ 7 ], particularly for various applications using superconductors [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ], cryogenic pressure vessels [ 19 ], etc. Moreover, DOFS and quasi-distributed optical fiber sensors (q-DOFS) expand their application field to wearable devices [ 20 ], integrated sensor-actuators [ 21 ], and biomedical areas [ 22 , 23 ].…”